New strategies for determination of transition metals by complexation ion-exchange chromatography and post column reaction

A method for the simultaneous determination of metals (Fe3+, Fe2+, Cu, Ni, Zn, Co, Cd, Mn and Pb) at mu g/l levels in environmental matrices is demonstrated. The metals are separated by ion chromatography on a mixed-bead ion-exchange column (IonPac CSSA) and detected by post-column reaction and spectrophotometric detection. The use of a gradient program (based on oxalic acid-hydrochloric acid-sodium chloride and sodium nitrate eluents) allows the separation of nine metals in a single run. The direct injection of a large volume of samples lowers the detection limits to below and/or few mu g/l. The chromatographic conditions and colour-development reaction were optimised. Two post-column reagents, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) and 4-(2-pyridylazo) resorcinol, were tested and detection limits were compared. The use of 5-Br-PADAP increased the sensibility for Cu, Cd, Zn and Mn. For the proposed method, linearity, reproducibility, detection limits and interference due to alkaline-earth metals (noticeably Mg and Ca) were discussed. Under the suggested chromatographic conditions Mg2+ and Ca2+ up to 0.2 g/l do not interfere with separation and quantitative analysis of the metals. The calibration graphs were linear (r(2)>0.986) in the range 5-5000 mu g/l. The application of the method to the determination of metals in coastal marine sediments is shown. (C) 1999 Published by Elsevier Science B.V. All rights reserved.